Chip cards are used for a large number of applications. Examples of application are what are known as SIM cards, which are used in mobile telephones. In this case, the chip card is usually accessed by means of contact via a standardized ISO interface. In accordance with ISO standard 7816, five prescribed signals are associated with contact areas in a contact array. Provision is made for a supply potential, a reference potential, a reset potential, a clock signal and a data signal to be applied. The contact array usually has six or eight contact areas, so that further signals can optionally be applied. A chip card controller, with which it is possible to communicate in accordance with the ISO standard, has appropriate connections to which standardized signals are applied.
To increase the performance and functionality of chip cards, the chip card may be provided with further circuit blocks, for example memory units. These circuit blocks are accessed in conventional circuit arrangements via further interfaces which are provided in addition to the ISO interface. Since conventional SIM chip card controllers do not have further interfaces, a proprietary chip with a second interface is usually provided.